Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter, and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Inflation expandable stents are crimped to their reduced diameter about the delivery catheter, maneuvered to the deployment site, and expanded to the vessel diameter by fluid inflation of a balloon positioned on the delivery catheter. The present invention is particularly concerned with delivery and deployment of inflation expandable stents.
There is currently a drive in the market to reduce the wall thickness of expandable coronary stents. Clinical results have shown that a reduced stent wall thickness improves vascular response.
There is also a market drive to make stents more flexible, allowing physicians to more easily maneuver stents through the bodily lumen, especially through the tortuous paths common in small vessels.
Thus, present stents commonly combine a thin wall thickness with high flexibility, which leads to various drawbacks associated with stent delivery. Stents with a reduced wall thickness typically have reduced strength in all directions. A stent with reduced strength has less ability to remain secure on the balloon and delivery catheter in the reduced state. Therefore, the stent has an increased risk of shifting positions on the catheter as it is maneuvered through the body. The stent must be able to securely maintain its axial position on the delivery catheter without translocation of its proximal or distal ends.
Reducing stent wall thickness may also reduce the axial strength of the stent. Lowered axial rigidity allows the stent to more easily pass through curved bodily vessels but can also lead to difficulty in stent placement during expansion.
When a stent with low axial rigidity is expanded by a balloon catheter, the stent may experience increased shortening or lengthening. If balloon inflation begins at the ends and continues inward, the deployed stent often has a shorter overall length after expansion. Conversely, if balloon inflation begins at the center and moves outwardly, the stent often experiences lengthening upon deployment.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al discusses an expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During expansion of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al. describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site.
These known methods typically release the stent early in the balloon inflation procedure and do not maintain the axial dimensions of the stent during inflation.
There remains a need for stent delivery systems that constrain the axial dimensions of the stent until the stent is fully expanded.
All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.